The storage capacity of hard disk drives is increasing in rapid fashion. In fact, the capacity of an average disk drive has doubled every 18 months, and, in recent years, has even outpaced the tremendous performance advances in the integrated circuit industry. In order to maintain this explosive increase in capacity, the components that make up the drives are quickly evolving and new technologies are being developed.
As storage densities increase, the distance between the read/write head and the disk surface decreases, since the signal that can be obtained from the data stored within the disk increases as the head moves closer to the disk. This evolution has progressed to the point that, in state-of-the-art drives, the head flies only a few billionths of a meter above the disk. If these dimensions are scaled to more physically tangible values, the system is comparable to a 747 jet flying only a few millimeters above the ground (source: Larry Bailey, “No More Hard Drive Crashes? The Interfacial Behavior of Perfluoropolyether Lubricants”, http://www.stanford.edu/group/i-rite/body bailey.html). In a system with tolerances this tight, occasional contact between the head and the disk is inevitable.
A typical disk drive includes substrate material, typically, glass or aluminum, and a number of adhesion-promotion layers, which form a metallic support structure, a magnetic layer for storing data, and finally a thin layer of hard, amorphous carbon. This thin carbon layer protects the soft magnetic layer from damage whenever the head impacts the surface of the disk. The surface of the carbon layer is coated with an extremely thin perfluoropolyether lubricant film. The purpose of this film is to minimize wear of the carbon layer when the head and disk come into contact.
As the magnetic spacing between the head and the disk gets tighter, the protective layer becomes even thinner. In a typical drive, the lubricant is only approximately one molecule thick. Despite this ultra-thin disposition, the lubricant film is very important to the durability of the drive. With lubricant in place, disks typically last years before wearing out, whereas without it, they wear out in a few days.
The lubricant layer also protects the data surface from corrosion and outgassing contaminants. A thinner protective film makes it more likely that in actual use, microscopic contaminants and moisture will penetrate to the magnetic layer. This can lead to corrosion and ultimately cause head crashes, making it impossible to read/write data. In the harsh environments to which handhelds and other mobile devices are exposed, this presents a serious problem and has been a major obstacle to developing greater data densities and wider applications for hard drive technology.
As a result of the foregoing problems, there exists a need for an apparatus and method for performing in-situ detection of lubricant depletion in a disk drive. There is also a need for performing an appropriate corrective action, once lubricant depletion has been detected in one or more zones on a disk.